Shock waves occur in fluid systems when a flow in the supply is quickly and abruptly closed or when a force in flow is suddenly changed. The fluid system is usually a liquid system, but sometimes also is a gas system. Such shock waves commonly occur when a valve is closed at an end of a piping system, resulting in a pressure wave propagating in the pipe, which is commonly referred to as a water hammer.
This closure of the supply or sudden change in momentum of the flow can cause major problems. For example, a buildup of water flow can be created resulting in a pressure spike that physically can rattle the pipes causing noise and vibration. This noise and vibration can often be heard and felt within a dwelling or building. The water hammer also produces stress on the pipes and components in the system, which can lead to failure in the system and water damage.
While the presence of water hammer cannot always be anticipated when planning plumbing layouts, it can be corrected. In particular, in order to prevent violent pipe noise, system failure, and damage, devices have been developed to provide the high pressure spike somewhere to go.
For example, shock suppressors have been developed to reduce the pressure spike in the system. Such shock suppressors, also referred to as water hammer arrestors, utilize a precharge of air to provide an air cell or air cushion that absorbs the pressure shock in the system. One example of a shock suppressor is an air chamber in the form of a vertical pipe located in a wall of piping at a point near a faucet. Another example of a shock suppressor is placement of a valve where the water-supply pipe exits the wall. The air chamber acts as cushions to prevent impact between the water and the piping. As the pressure shock enters the shock suppressor, the air cushion compresses, the air pressure increases, and the shock is absorbed. Such shock suppressors can be incorporated in a system via a valve or the like. Such designs generally include a movable piston that is sealed to the inner diameter of the pipe. The air charge on one side of the piston provides resistance to water pressure on the other side of the piston until the water pressure increases above the air charge pressure. When this occurs, the expanded water pushes on the piston and enters the pipe.
Such shock suppressors have may associated disadvantages, including leakage of air charge, which results in loss of pressure acceptance function. Also, such seals are typically dynamic o-ring seals, which have the potential to lose their sealing capability with debris or due to a poor surface condition of the inner diameter of the pipe or the o-ring.
Further shock absorbers have been developed which include a flexible diaphragm separating the air cushion from the water stream that enters the shock absorber. One example of such a shock absorber is depicted in FIGS. 1A-1B. Such a shock absorber may be located extending from a wall of piping such that, as the water flow is abruptly stopped or changed, the water can enter the shock absorber. As the water enters the shock absorber, it comes into contact with the diaphragm which is pushed towards the air cushion on a side opposite the water side to thereby compress the air cushion. This contact with the diaphragm and compression of the air cushion acts to absorb the pressure shock.
While such shock suppressors are capable of reducing water hammer and addressing the problems resulting from water hammer, they are susceptible to losing their ability to absorb pressure shock and volume expansion over time. In particular, the diaphragm often weakens and fails, for example, at an outer edge or at an inside portion along the diaphragm. This failure reduces and often eliminates the ability of the shock suppressor to absorb water and pressure shock. Further, if the diaphragm fails and allows water to pass through into the air cushion, the water entering the air cushion side comes into contact with what is generally an unprotected steel or corrodible metal housing, leading to corrosion and rust in the system. As such, regular maintenance of this type of shock absorber is required, often resulting in the need to replace the entire system. In addition, in these shock suppressors, a precharge of air is required to provide the air cushion. This complicates the design and application and maintenance of the shock absorber.